md-go-validator v0.3.0

Changelog

• ecda347 ci: expand dogfood scope and add nix flake check job
• c5830b8 docs(changelog): cut v0.3.0 release
• 9d0f8fb docs(changelog): record v0.13.0 release and capture all unreleased changes
• 7c29371 docs(status): add comprehensive post-v0.2.0 release status report
• 52aeb6c docs(status): add post-code-review comprehensive status report
• 21ee8fa docs(status): apply oxfmt formatting to v0.2.0 status report
• e835a74 docs(status): reformat tables for consistency in status report
• 6d269dd feat: add STDIN support, structured exit codes, and ErrorCode threading
• 84b944d fix(cli): correct help text that falsely claimed external tools required
• 869d2ef fix(nix): add maintainer to package meta
• e349385 fix(nix): remove useless parentheses flagged by statix
• cbaa922 fix(nix): restore broken build, DRY package definition, fix overlay
• 5dc7606 fix(nix): update vendorHash for go.sum cleanup, add platforms meta
• db0f022 fix(types): enforce Result StatusError invariant and guard report panic
• 451d016 refactor(context): remove dead limit fields from ContextConfig
• c616c98 refactor(extractor): stop pre-marking blocks valid before validation
• d4a59e5 refactor(languages): consistent ValidationError receivers and dedupe TreeSitterValidator
• 55d2fc9 refactor(output): consolidate ANSI constants and fix quiet summary
• c8ad4ca refactor(validator): single source of truth for file types and simpler concurrency
• 16ec967 refactor: deduplicate tests, centralise nil-guards, and adopt table-driven patterns
• dd125fc refactor: update Go dependencies, update source code, update assets